Embedding Green Chemistry principles into the Formula of a Hydrate lab

12 principles of green chemistry

A traditional hydrate lab used to demonstrate the formula of a hydrate is the dehydration of copper sulfate pentahydrate. Most use a Bunsen burner as a heat source. At King Philip Regional High School in Wrentham, MA, we in the chemistry department have created a goal to weave green chemistry throughout our curriculum, so we ask students to analyze every lab, identifying where it meets green chemistry principles and where it could be improved. While copper sulfate pentahydrate is not one of the worst culprits when it comes to disposal, we wondered how we could engage students in the greening of this lab. As such, we have substituted the use of Epsom salts or magnesium sulfate heptahydrate and use a hot plate instead of a Bunsen burner.

We were worried that the elimination of the color change seen with the dehydration of the copper compound would lessen the impact of the lab, but we were pleasantly surprised that, while a color change didn’t occur, definite physical changes were evident. Students were able to note a change in texture as well as a “popcorn effect” due to the removal of the water. Using the hot plate allowed for better control of the slow dehydration, also enabling students to obtain better results than they did with traditional the lab.

 

 

After using this "greener" replacement lab for the past two years, we have found that the vast majority of our students have been able to come up with the correct calculation of the formula. The added bonus to this replacement lab is that it generates rich discussions on the application of green chemistry principles. Students easily explain why the Epsom salt is less hazardous in terms of potential toxicity. At the same time, substitution of the hot plate has led to deep discussions on the safety of the hot plate over the burner vs. the need to heat the substance for a longer period at a low temperature. Our students were able to relate these discussions to several of the principles of green chemistry, including:

  • Principle 3, as the Epsom salt is less hazardous to humans and the environment
  • Principle 4, as Epsom salt serves the same function as the copper sulfate while reducing risk
  • Principle 7, as the Epsom salt can technically be reused once it is rehydrated
  • Principle 12, as the use of a less hazardous substance reduces the risk of accident

Find more information about greener replacement labs  by visiting the Beyond Benign website

The American Chemical Society provides details about the 12 principles of green chemistry. You can download a pocket sized list of the principles on the same webpage.

Compound Interest created a handy version of the green chemistry principles.

Another take on a modified hydrate lab that could be tweaked by replacing copper II sulfate pentahydrate with magnesium sulfate heptahydrate : Cookbook to Inquiry -- Another Attempt

 

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Comments 4

Jordan Smith's picture
Jordan Smith | Tue, 04/03/2018 - 14:16

I've used Epsom salt for this sort of lab forever and never even thought about reusing it.  I can't believe that never occurred to me.  Thanks for sharing a great idea!

John Muench's picture
John Muench | Thu, 04/05/2018 - 13:35

We use Alum that we made from converting Aluminum cans into this product.  Theoretically, you can collect the de-hydrated product, dissolve back into water, and then evaporate the water to recover your starting material.  Alum is used in the water treatment process so it is benign.  Additionally, the compound has 12 waters so it shows a large change in mass.

Bob Worley's picture
Bob Worley | Sat, 04/07/2018 - 01:57

On the surface, using the Alum that has been recycled from aluminum cans may seem benign. I have to disagree. Please read  https://en.wikipedia.org/wiki/Camelford_water_pollution_incident

This event was caused huge concern to the county of Cornwall. Please remember that it is the dose that that makes the poison. To make the alum from aluminium cans, one has to use 1.5M potassium hydroxide and 9M sulfuric acid. Is this green compared to recycling the can in the appropriate receptacle and letting industry do its job. Of course, there are safety concerns attached to using the chemicals required for extraction of the alum from the cans. 

Just to allay your fears, I do advocate green chemistry but you do have to be careful to explore all the avenues as those who do not advocate a green approach will soon demolish your ideas. Critics of some of my microchemistry do this quite often so I have to counter that "every procedure I do in microchemistry has to have an added chemical benefit". (www.microchemuk.weebly.com )

Cheers from accross the pond

Bob

Deanna Cullen's picture
Deanna Cullen | Sat, 04/07/2018 - 10:22

Thanks for this information, Bob. After reading your comment, I found several labs that supported your claim that the extraction of alum from aluminum cans requires concentrations of sulfuric acid and potassium hydroxide that concern me. I wonder if a greener option has been developed by anyone.